Despite its rarity, hypertension caused by oral contraceptives continues to be a major public health problem because of the many millions of women involved. Since underlying mechanisms are poorly understood, studies are proposed to test the hypothesis that contraceptive steroids induce hypertension only when other predisposing factors are present. The cardiovascular effects of orally-administered Enovid and its constituents, mestranol and norethynodrel, will be recorded in awake normotensive and hypertensive (e.g., renal, DOCA, neurogenic, or spontaneous) rats to determine whether or not chronic treatment potentiates the development and maintenance of various blood pressure elevations. Based on our previous finding that Enovid increases pressor responsiveness to hypothalamic stimulation, the cardiovascular effects of destroying hypothalamic centers will be recorded in normotensive and hypertensive rats pretreated with contraceptive steroids. In other experiments, these drugs will be injected or implanted into hypothalamic pressor or depressor centers to determine possible direct or indirect effects on cardiovascular function. Hemodynamic mechanisms involved in the pressor effect will be identified by using chronically-implanted electromagnetic flowmeters to record aortic flow. Possible indirect effects which contraceptive steroids produce by increasing cardiovascular reactivity or sympathetic vasomotor activity will also be tested. By identifying the pressor mechanisms involved, the proposed studies may improve understanding of oral contraceptive hypertension and provide a rational basis for its prophylactic management.